Yeah, I'm thinking either the person reposting is slightly confused, or maybe the original posting is a bit off.

I've heard of people putting in alder cones and (I think?) almond leaves. I think the claim was that these specific leaves/cones had anti-fungal properties, and were good for breeding tanks, as it would lessen the risk of fungus damaging eggs.

*shrugs* That's about the only thing that comes to mind as to "conditioning water" with leaves- and maybe a bit of a blackwater effect.